It took only 250 years for democracy to disintegrate in ancient Athens. A wholly new form of government had been invented there in which the people ruled themselves. That constitution proved marvelously effective. Athens grew in wealth and capacity, fought off the Persian challenge, established itself as the leading power in the known world and produced treasures of architecture, philosophy and art that bedazzle to this day. But when privilege, corruption and mismanagement took hold, the lights went out.

It would be 2,000 years before democracy was reinvented in the U.S. Constitution, now as representative democracy. Again, government by popular consent proved ingenious. The United States grew into the world’s leading power — economically, culturally and militarily. In Europe, democracies overtook authoritarian monarchies and fascist and communist dictatorships. In recent decades, democracy’s spread has made the remaining autocracies a minority.

The second democratic experiment is approaching 250 years. It has been as successful as the first. But the lesson from Athens is that success does not breed success. Democracy is not the default. It is a form of government that must be created with determination and that will disintegrate unless nurtured. In the United States and Britain, democracy is disintegrating when it should be nurtured by leadership. If the lights go out in the model democracies, they will not stay on elsewhere.

It’s not enough for governments to simply be democratic; they must deliver or decay. In Britain, government is increasingly ineffectual. The constitutional scholar Anthony King has described it as declining from “order” to “mess” in less than 30 years. During 10 years of New Labor rule, that proposition was tested and confirmed. In 1997 a new government was voted in with a mandate and determination to turn the tide on Thatcherite inequality. It was given all the parliamentary power a democratic government could dream of and benefited from 10 years of steady economic growth. But a strong government was defeated by a weak system of governance.

The next government, a center-right coalition, has proved itself equally unable. It was supposed to repair damage from the economic crisis but has responded with inaction on the causes of crisis, in a monopolistic financial-services sector, and with a brand of austerity that protects the privileged at the expense of the poor. Again, what has transpired is inability rather than ill will. Both these governments came up against concentrations of economic power that have become politically unmanageable.

Meanwhile, the health of the U.S. system is even worse than it looks. The three branches of government are designed to deliver through checks and balances. But balance has become gridlock, and the United States is not getting the governance it needs. Power has been sucked out of the constitutional system and usurped by actors such as PACs, think tanks, media and lobbying organizations.

In the age of mega-expensive politics, candidates depend on sponsors to fund permanent campaigns. When money is allowed to transgress from markets, where it belongs, to politics, where it has no business, those who control it gain power to decide who the successful candidates will be — those they wish to fund — and what they can decide once they are in office. Rich supporters get two swings at influencing politics, one as voters and one as donors. Others have only the vote, a power that diminishes as political inflation deflates its value.

In Athens, democracy disintegrated when the rich grew super-rich, refused to play by the rules and undermined the established system of government. That is the point that the United States and Britain have reached.

Nearly a century ago, when capitalist democracy was in a crisis not unlike the present one, Supreme Court Justice Louis Brandeis warned: “We may have democracy, or we may have wealth concentrated in the hands of a few, but we can’t have both.” Democracy weathered that storm for two reasons: It is not inequality as such that destroys democracy but the more recent combination of inequality and transgression. Furthermore, democracy was then able to learn from crisis. The New Deal tempered economic free-for-all, primarily through the 1933 Banking Act, and gave the smallfolk new social securities.

The lesson from Athens is that success breeds complacency. People, notably those in privilege, stopped caring, and democracy was neglected. Six years after the global economic crisis, the signs from the model democracies are that those in privilege are unable to care and that our systems are unable to learn. The crisis started in out-of-control financial services industries in the United States and Britain, but control has not been reasserted. Economic inequality has followed through to political inequality, and democratic government is bereft of power and capacity. Brandeis was not wrong; he was ahead of his time.

Stein Ringen is an emeritus professor at Oxford University and the author of “Nation of Devils: Democratic Leadership and the Problem of Obedience.” He wrote this column for the Washington Post.

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